Electromagnetic gun.



No. 754,637. PTBNTED MAR. 15, 1904.

' BIRKELAND. v

ELEG'I'R0ISIIAGrII-KIIGv GUN.

APPLICATION FILED JYAN. 2, 1902. A N0 MODEL. 6 SHEETS-BHEBT'Z. i

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PATENTBD MAR. l5, 1904'.

K.l BIRKELAND.

ELEGTROMAGNETIG GUN.

APPLIoATIoN FILED JAN. 2, 1902.

6 SHEETS-SHEET 3.

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110.754,63?. l PATENTBD MAR-15,1904.

. K.,B1RK`BLAND. BLEGTROMAGNETIG GUN.

. yAP-PLIM'I'ION FILED JAN. 2, 1902.

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PATENTBD MAR. 15, V1904.

K. BIRKELAND.- BLECTROMAGNBTIG GUN.

APBLIUATION FILED JAN. 2, 1902.

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um C" UNITED STATES atented. March 15,

PATENT OFFICE.

E'LGTROMAGNETIC GUN.

SPECIFICATION forming part of Letters Patent No. 754,637, dated March 15564; Application filed January y2, 1902. Serial No. 88,189. (No model.)

Toa/ZZ whom/ it may concern: l

Be it known that I, KnIsTIAN BIRKELAND, a subject of the King of Sweden and Norway, residing at Christiania, Norway, (whose post-I oflice address is the same,) have invented certain new and useful Improvements in Electro: magnetic Guns; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others slrilledin the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters and. figures of reference marked thereon, which form a part of this specification. f

The present invention relates to an electromagnetic gun. p

It has heretofore been considered practically impossible to` construct an electromagnetic gun-that is to say, to'produce a gun of this kind which would throw a service projectile with service velocities-because of the fact i that the modern methods of electrical calcula-k ti'on would indicate that in order` to obtain service velocities with service projectiles an enormous number of windings would be required, thus involving the use of a 'barrel whose length would be prohibitory. I have found, however, that it is practicable to construct a gun of this kind which will meet all service requirements and which will have many advantages over the usual powder-guns.

` My invention is based upon the fact that the magnetic eect of a current isa function of the current only, while the rate of increase of the temperature of a coil carrying such current depends upon a number-of factors other than the current. As aresult of this the magnetic effect of a current in a coil will attain a maximum in advance of the temperature of the coil. Consequently, as I have observed, an enormoiis magnetic eii'cct may be obtained in a practical manner by supplying an abnormally heavy current to a coil and then cutting off the current from the coil before the temperature of the 'said coil has reached `such a point as to injure or destroy the coil. I have found, for instance, that an iron rod having a length of about ten inches and a sectional area of one square inch when placed about midway in a solenoid of the same length weighing about twenty-four pounds and hav-Y ing an inner diameter of nearly two miles andan outer. diameter of four and one-half inches was drawn into the solenoid withaforce of about one hundred and seventy pounds, when a current of two hundred and thirty amperes was sent through the solenoid. The heat generated in the coil at the end of one second after the current was turned on was not so great but that the solenoid would have safely withstood ten times as heavy a current for one-tenth of a second, in which case the force acting upon the rod would be about seventeen hundred pounds per square inch. Furthermore, the above calculation is based upon the supposition that the iron rod in the k'above experiment was saturated with magnetism. If this be not the case, the magnetic force produced by the multiplied amperage would be still geater relatively. A calculation shows that a single pole of the said iron rod when saturated with magnetism should be drawn into the solenoid with a force of the description hereinafter when the term projectile is employed this is to `be understood to be either an iron rod or a body of coils arranged in some suitable way.

`The above-named facts I utilize in constructing a gun in which the projectile is thrown by aid of electromagnetism, the gunbarrel being arranged as a tube of sufficient length surrounded by solenoids. Means is provided for supplying these solenoids with an abnormally heavy current-that is to say, a current beyond the capacity of the solenoid as calculated by the methods now in vogue with electrical engineers for determining the safe carrying capacity of a coil-and means is also provided for cutting off the current from the solenoids before the said current has had time to raise the temperature of the solenoid to a point sufficient to destroy it. The control of the cutting out of these solenoids may be effected by aid of circuit-breakers ar- IOO ranged outside the gun; but I prefer effecting the cutting out of the solenoids automatically by aid of the projectile itself, the projectile.

lenoids, which contrary tension or counter' electromotive force may be made to act at the moment of breaking the circuit, so that the current at this moment actually has no energy. The circuit-breaking devices should therefore be arranged so as to be also in conformity herewith. As to eventual sparks, it

must be remarked that all such are at oncer blown out by the immense draft resulting from the projectile motion in the gun-barrel.

This invention is especially adapted to throwing projectiles containing large quantities of high explosives, it being possible in this way to put the projectile into motion and increase the driving force until the desired initial velocity is reached, whereupon the force may be decreased gradually, so that all sudden shocks of the projectile thereby are avoided.

My invention will now be described in connection with the accompanying drawings, in which- Figure 1 is a diagrammatic view of the rear portion of a gun embodying my invention, and Fig. 2 a detail cross-section of the barrel. Fig. 3 represents a longitudinal section through part of a gunin which a projectile is moving. Fig. 4 is a cross-section on the lines 4 4, Fig.` 3. Fig. 5 is an enlarged cross-section vthrough the part of the tube which carries the circuit-breakers. Fig. 6 is a sectional plan of the same. Figs. 7 and 8 are diagrams showing two different forms of automatic main circuit-breaking arrangements. `is a diagram showing a third form of automatic main circuit breaking arrangement. Fig. 10 is a diagram of a solenoid projectile. Fig. 11 is a sectional view of a detail of the same. Figs. 12 and 13 are diagrams illustrating the manner in which the current is cut off from the solenoids to avoid destructive sparking, and Fig. 14 a diagrammatic view of an other embodiment of my invention. Before describing in a detailed manner the electrical and mechanical constructions preferably made use of when carrying out my invention I shall explain the general idea in a more concrete form, reference being had to Figs. 1 and 2 of the annexed drawings.

Fig. 1 of the accompanying drawings shows a diagram of the breech end of a gun. Fig.

kan insulating material.

Fig. 9 l

2 is a cross-section. The projectile 0;, which is shown as being an iron projectile, has just begun its passage through the gun tube or barrel. This tube, which may suitably be made of bronze or steel, is slotted on one side along its whole length, as shown in the sectional view Fig. 2, and surrounded by solenoids c. The solenoids are connected in series .by two, and each group of two solenoids is arranged on a" reel d, threaded on the barrel-tube b. The elementary solenoids of each reel are connected with each other in the way shown in the diagram Fig. 1, the connection at the inside of the solenoids consisting ofcontact arms a, extending into the above-named slot of the barrel-tube. In order to facilitate the understanding of the diagram, the pairs of contact-arms are shown arranged longitudinally instead of laterally. The said pairs of contact-arms may be separated, and thereby the group of solenoids to which they belongv cut out by aid of a wedgeshaped nose f, carried by a slider g, made of The said slider, carrying the wedge-shaped nose f, slides in suitable guides L, provided in the inside surface of the barrel-tube, and, being provided with a rib z' on its back end, is carried along with the projectile, the latter having a circumferential groove 7c, into which the said rib a' fits. In the position of parts shown in the diagramniatical view Fig. 1 the nose is just severing the contact-arms of the third group of solenoids,thereby cutting out this grou'p. In order to saturate the projectile (if it be of iron) with mag- .netism before it begins its passage through the gun-barrel, I may arrange on the back end of the gun-tube an electric coil s with a separate current source. During this saturating process the projectile may be put into rotation by the aid of a motor having its driving-shaft loosely coupled with the back end of the projectile.

It will be evident that I may carry out my invention in a great many different ways without departing from the principles thereof. In the embodiment which has now been explained only for the sake of illustrating the principle of the invention it was assumed that from lthe beginning current was iiowing through all of the solenoids. I may, however, also modify my invention so as to send current through the solenoids in front of the projectile just in time before the projectile passes. I may make use of solenoids connected in parallel, or I may arrange groups of solenoids in which the elementary solenoids are in series while the groups are connected in parallel, or the whole set of solenoids may be connected in series, so that a continual winding is obtained. The

. necessary energy may be obtained from a system-of generators constructed especially for this purpose. These generators may be provided with large -iiy-wheels, while the driving machinery may be given relatively small IOO IIO

'for all sorts of these electromagnetic guns.

dimensions. A system of ten such dynamos, each of which in the moment in which they are short circuited, for instance, produces three thousand volts and thirty thousand'amperes, would be suficient to deliver power to a whole battery of the largest guns. AA part of the kinetic energy of the fly-wheels would at the moment of closing the gun-circuit be instantly transmitted to the projectile. Also accumulators might be used as a current source A battery of accumulators for this purpose would in certain cases be of great importance, in that by use of such it would be possible in a limited space of time .to throw a great many projectiles. Acucmulators endure a relatively large number of short-circuitings within a limited space of time. A battery of accumulators might, therefore, be kept in dry condition, so that they could be filled and formed in the course of a few days, when the occasion for their use requires.

If suitable currentsources are used having very low internal resistance, a gun of large' the internal resistance of the current source and so that the projectile when passing through the gun induces sufficiently-great counter electromotive force to make the commercial efiiciency satisfactory. Out of a battery of accumulators for this purpose a current of one hundred thousand amperes by two thousand volts may easily be taken. One pole of the battery may, for instance, be connected with the bronze tube and the other pole with the winding at the front end'of the gun, and the short -circuiting of the accumulator through the winding may in this case preferably be caused by means of a contactpiece .which electrically connects the inner side of the winding with the bronze tube. This manner of carrying out the invention is illustrated in the diagram Fig. 14, which explains itself. In this case the'windings that counteract the motion of the projectile .are cut out from behind at the proper moment, thereby avoiding the formation of sparks. T mouth of the gun will there be formed a spark, which is blown out. The insulations may be so constructed that the gun will withstand considerable heating. This kind of gun is especially suitable when a solenoid projectile is used caf pable of setting up a very great counter electromotive force in the solenoids of the gun. This may be so arranged that this counter electromotive force at the moment the projectile leaves the gun makes the solenoids of the gun approximately free from current, so that the final breaking of 'the current may be effected Only when the projectile leaves the without diiculty. If the gun is to be very long, it may be suitable to divide the said continuous coilv into two or more coils arranged one behind the other and in parallel'with the source of current. As above mentioned, the front end of the continuous coil or coils is connected with the source of current. The back endr is open. If the coil is divided in two .or more coils, the back ends of each of these coils are carried rearwardly along the gun to its back end, where they are open. The said contact-piece slides along these ends, so that all of them will be in circuit at the starting of the projectile. In order to avoid a shock at the moment the projectile leaves the tube, the solenoids may be so arranged that the force exerted on the projectile decreases as' the latter approaches the exit.

I will now proceed to explain the nature of some of the mechanical and electrical arrange-` ments which I preferably make use of 1n carrying out my invention.

Inthe form of gun illustrated in Figs-.3 and 4 of the drawings the solenoids 20 are arranged in groups of, say, three hundred in each group. The elementary solenoids of these groups are connected in parallel to the mains 21 22. Each of the solenoids is provided with a current-breaker, andI prefer to cut the'wirein 'the middle of each solenoid and connect the ends with springs arranged in slots near the inside of the gun-tube, as will hereinafter be fully described. 10 is the tube of the gun, preferably made of bronze or steel. It is provided with a longitudinal slot along its whole length, and this slot is filled with a block 11 of insulating material. In this block are provided four grooves 12, in which the current-breakers or contact-springs 13 are secured. The reason why more than one groove is made use of is that Il am able, in this manner, to obtain so large a distance between the consecutive pairs of springs that they may be given a suitable length.. As shown, I arrange the springs in four rows, with insulating-material between each row, so that the distance between the contact-l springs in each row will be four times the length of each solenoid. This will be clearly seen from Fig. 6. 20 -iand 2O are the abovementioned ends of the solenoid, which are carried down through the insulating-block to the springs 13, which are preferably placed in recesses 14 in the sides of the grooves 12. The projectile 1- is provided with two or more rings 2, placed in annular grooves in the pro-` jectile. These rings, in which the projectile may rotate, (as in journals,) are provided with three peripheral lugs 3, which iit into longitudinal guide-grooves 4 in the barrel-tube, and with a fourth lug 5, the peripheral length of which corresponds with the distance between the external sides kof the outermost grooves 12. 7 represents long rods or slides of insulating material, one fitting into each of the IOO IIO

IZO

said grooves 12 and provided with notches', l

that fit over the said lug 5 on each of the rings 2. It will be seen that when the projectile moves forward the lugs 5 will take the slides 7 along through their respective grooves. At the forward end theseslides are keyshaped and provided with a covering 8 of conducting material. The action of these slides on the contact-springs will be clearly understood from Fig. 6. When the projectile has left the barrel, the slides will drop off. The length of the same is preferably made so it will be somewhat longer than the length of each group of three hundred (or other number) solenoids. The slides hold the contacts broken in the whole length of the slide, and the same is preferably so placed on the projectile that the solenoids are cut out some distance in front of the middle of the projectile. In Fig. 3 the contact-springs are not shown; but it is indicated in a clear way which ofthe solenoids are closed and which open. As shown, the solenoids behind the slide are closed as the projectile passes forward. On account of the time it will take for the springs to go together after the slide has passed, the solenoids will be open some time after the passage of the projectile, even if the slide is not made so long as shown. In order to cut 0E the current for the part of the gun behind the projectile, I may make use of circuitbreakers placed in the mains leading to each group of three hundred solenoids and arrange n these circuit-breakers insuch manner that the current in each group is broken just at the moment the last solenoid of a group has been cut out by the opening of its springcontact 13.

One manner of aifecting the automatic opening of the main circuit-breakers is illustrated in Fig. 7. In this ligure a diagram of the electrical connections is shown in connection with a part of a longitudinal section through the gun-barrel along one of the above-mentioned guide-grooves 4, in which a lug 3 on one of the rings 2 is moving. In the main 21 is arranged a circuit-breaking arm 23, which swings on the center 24 and is provided with an arm 25, -serving as armature for the electromagnet 26. The winding of the latter is connected with the last one of a group of solenoids, so that as long as this solenoid is closed, as shown, the electromagnet will atf tract the arm 25, and thereby hold the circuit ingl out through the gun-barrel and its surrounding solenoids and ending in contact with an arm 30 on the circuit-breaker 23. When the lug 3 passes the said spring 28, it will cause the pusher-rod 29 to be pressed against the arm 30, and thereby give the arm the necessary impulse, so that the spring 27 may be able to effect the withdrawal of the armature 25 rapidly.

Another manner of eiecting the automatic breaking of the main circuit-breakers is illustrated in Fig. 8. In this instance I make use of the recoiling action of one of the solenoids in each group. I place one of the solenoids 31 in a separate reel 32, which is mounted loosely on the gun-barrel, so that it may move in the axial direction of the gun about as much as one-fourth or one-half of an inch between two neighboring solenoids, springs 33 being utilized to hold the solenoid in its normal forward position. 34 -is a lug on the outside of solenoid. provided with an arm 36, extending downward behind the said lug 34, and with another arm 37, against which a spring 38 acts, so as to hold the breaker in its closed position. When the projectile moves on and approaches the solenoid 31, the recoil of -the latter will overcome the tension of the spring 33, so that the solenoid will move backward, and thereby the lug 34 will hit the arm 36, and the arm 37 will thereby be pressed down past the end of the spring 38, so that the circuit 21 22 will be opened. 'Of course it will be most preferable to arrange a set of four or more circuit-breakers symmetrically around the solenoid. A third manner of eifectin'g this automatic breaking of the main circuit-breakers is illustrated in Fig. 9. In this instance I make use of the gun-barrel itself as a stationary contact, to which one end of the main conductor is connected, and of the projectile as a movable contact-piece. In Fig. 9, 41 42 represent copper rods mounted on the inside of the gun-barrel, insulated from the latter and from each other. Of these rods there are as many as there are groups of solenoids, and eacli of them extends from the rear end of the gun to the end of the group to which it belongs. To these rods are connected the leading-in wires of each solenoid of the respective group, as indicated, while the other leading-n wire of each solenoid is connected to the main 21. The other main 22() is connected with the gun-barrel. The projectile carries brushes 45,whicl1 are in contact with all of the rods 4l 42, &c. It will be-seen that the brushes will establish a circuit through the projectile 1, the barrel l0, conductors 220 210, solenoids 20, and conductorrods 41 42, &c., and, as the projectile moves, one after the other of these rods and the solenoids connected therewith will be cut out of the circuit. If it is not desired to have the circuit set up for the whole gun at once, but only successively as it is needed, this result may 35 is the circuit-breaker, it being IOO IIO

be reached by not letting Aall the rods extend back to the rear end of the gun, but only to some distance in front of the same, according to the solenoid group to which it belongs.

As to the dimensions which may be given to guns constructed according to my invention, the fol lowing example may he mentioned. For throwing an iron projectile weighing two tons and containing one thousand pounds nitrogelatin at an initial speed of one thousand feet per'second I make use of a gun of a length of about ninety feet, the projectile being about nine feet long and having a diameter of about nineteen inches. The gun-solenoids may be made up of square wire, each solenoid containing seven hundred and twenty windings of a resistance of fifteen ohms. rIhe length of each solenoid is made about three-eighths of an inch and the height (radial dimension) about eight inches. With an electromotive force of three thousand volts this will give a current of two hundred amperes. If the current is set up simultaneously in all the solenoids, (there will be about three thousand elementary solenoids) this will require altogether six hundred thousand amperes, and the suction acting on the projectile will be about two thousand live hundred pounds per square inch of the cross-sectional area of the projectile. A calculation shows that when a firing is to take place the current should be set up one-seventh of a second before the firing. The projectile is then set free, and it will pass the barrel in the course of one-fifth of a second. The current has then been on the outermost solenoid about one-third of a second. If, however, a construction is used in which all the groups of solenoids are not at once set up, (for instance, in th'e manner mentioned with reference to Fig. 9,) less than half the current will be used for the same effect, and the generation of heat in the outermost solenoids will be reduced.

As stated, I may. also make use of a projectile the body of which consists to a substantial extent of solenoid-windings, through which a current is passed during the passage of the projectile through the barrel. By using a projectile provided with such windings I obtain a multiplied effect. The driving force may in this instance rise to sixteen times that obtained with a projectile of soft iron only. The current may be fed to the coils of the projectile .through contact-rods arranged on the inside of the barrel. Fig. 10 is a diagram of a projectile of this kind, showing the elect rical connections and arrangements. The projectile is supposed to be constructed as before described or in any other suitable manner as regards the .circuitbreaking arrangements, Sac. In the diagram, 50 represents the barrel; 5l and 52, contact-rods mounted somewhere on the inside of the barrel, extending the entire length of and insulated from the barrel. 53 is the projectile. It may be made of steel and hollow, so that it can carry explosives. Around the central part of the projectile are placed solenoids 54, constructed, preferably, as short elementary s0- lenoids, which are connected in parallel. The Y current passes from the conductor 5l through the ring 55, to the wire 56 through the solenoids, to the wire 57 and from this through the ring 58 to the conductor 52. Toillustrate how the contacts in the rings' 55 and 58 may be arranged, I have shown a section in Fig. 11 through one of these rings. 55 is the ring. In the periphery of the same is placed a contact 60, insulated from the ring and sliding against the conductor 51. On the face of the ring is placed, in an annular groove and insulated from the ring, a contact-ring 6l, electrically connected with the contact 60, as shown. A similar contact-ring 62 is placed in a similar manner in the face of the groove in the projectile in which the ring 55 rests, and the rings 61 and 62 are made to be in contact with each other. To this ring 62 the leading-in Wire or cable 56 is secured, to which the solenoids 54 are connected in parallel, as before mentioned. It has been stated above when speaking about the breaking of the current in each of the solenoids that this may be performed without the forming of sparks, because the counter electromotive force induced by the projectile in the solenoids will reduce or entirely counteract the electromotive force of the main current. In orderth-at this very important point may be clearly understood, I will explain more fully the phenomena taking place in the gun, reference being had to the diagram Fig. l2. If the axis t ct of the diagram represents the length of the gun, the

driving force acting on the projectile at any point of its movement may be represented by a line d d', which line, as the drivingforce at the beginning (a d) is the same as that at the end, (a d,) will be parallel with the axis. As soon as the projectile has begun its movement it will induce a wave of a contrary tension or counter electromotive force, the maximum value of which will be increasing from 0 to many times as greatas the driving force, and

this maximum contrary tension or counter' electromotive force may therefore be represented by aline t c.- VAt a certain point a@ the value of said counter electromotive force will have reached that of the driving ,forcethat is to say, a@ c@ will be equal to ct@ (ZO-and from this point it will bey seenvthat it will be possible to break the current without sparks being formed. The induced counter electromotive force will set up an opposed current IOO IIO

the intensity of which will depend upon the said counter electromotive force and the time in which it actsthat is to say, the time which the magnetic pole takes to pass lthe solenoid in question. As this time will be so much the less the nearer the projectile is to the mouth of the gun, where the counter electromotive force is so much greater, it will be found by calculation that the opposed current will be ISO ` movement at @o as at the end.

amperes, so that the driving-current at the A-moment of breaking will be about one hunl Hdred and ten amperes.

The line ct cl in the diagram just referred to represents, asmen- Aforce in each solenoid.

tioned, the maximum counter electromotive terelectromotive force will be reached just when the forwardmagnetic pole of the projectile passes the solenoidthat is to say,

lwhen the windings of the solenoid are traversed by a maximum'of lines of force in a unit "of time. n "Referring to the diagram Fig. 13, s reprevsents a succession of solenoids, and p the for- Vabout at the point 13.

ward'p'ole of the `projectile moving in the direction of the arrow. The curve t will then represent the counter electromotive force produced by the forward pole in the solenoids embraced by the curveat the moment considered. In the solenoid S8 the counter electromotive force will be greatest, and it would therefore be most advantageous in regard to the avoiding of sparks to break the circuit at this point; but this, however, is not economical, because the said solenoid is still exerting a pull on the iron mass of the projectile.` Hence the breaking' will most'- advantageously be performed At said point a considerable reduction of the counter electromotive force has taken place; but it will nevertheless be at least as great as the driving force.

The breaking at this point is, however, at all events more advantageous, as the opposed current will be stronger at this point than at the point when the counter electromotive force has its maximum on account of the time necessary for setting up the current-that is to say, owing to the lag of the current behind the impressed electromotive force. 45

Also as regards the question of economy it will be an advantage to let the opposed current grow up to the intensity of the driving-current. I may, however, in some instance make use of 1 a speclal method for causing the maximum of counter electromotive force to act at the momentof breaking the circuit, in that I estab- Such pieces carried by the circuit-breaking rod of the projectile and establishing momentarily lelectric connection between the solenoid from which the current is to be cut 0E (.913) and that one' of the preceding -solenoids having at that moment the maximum counter electromotive force (ss). If the counter electromotive force were great enough, as when employing solenv'oid projectiles, then it would be able to set up an y'opposed current of such intensity that the total' current would be v0 in the moment This maximum coun-- of breaking the circuit. In this case the projectile would in a veryvshort time have consumed all the electrical energy which had been used to set up the current in the windings. This fact is of great importance for the question of economy. I might increase the self-induction in the solenoids by placing soft-iron rods on the outside of the gun, whereby the energy required for setting up the current would be vgreatly increased and whereby so much more energy could in this way be disposed of in each of the elementary solenoidsthat is to say, by being transferred to the projectile at the moment itr passed the solenoid.

Having thus fully described my invention, what I claim as new, and desire to secure by Letters Patent, is-

'1. In an electromagnetic gun, the combination, with aA gun-barrel, a plurality of solenoidwindingssurrounding said barrel, and means for supplying current to said windings, of a series of circuit-closers arranged to close the circuit of the respective windings, a projectile arranged to move inside the gun-barrel and progressively generate a counter electromotive force in the solenoid-windings, and means for progressively opening the circuit-closers of the respective windings, each at that moment when the induced counter-current in its corresponding winding is substantially equal to the current produced by the direct electrocircuit of the respective windings, a projectile arranged to move inside the gun-barrel and progressively generate a counter electromotive force in the windings, and means operated by the projectile and arranged to progressively open the circuit-breakers of the respective windings, each at that moment when the induced counter-current in the-winding is substantially equal to the current produced by the direct electromotive force.

3. The combination, with a barrel provided with a longitudinal slot, a plurality of solenoidwindings surrounding the barrel and means for energizing said windings, of a strip of insulating material mounted in said slot and a plurality of circuit-breakersconnected to said solenoids and mounted on said strip.

4. In an electromagnetic gun in combination, solenoid-windings, a barrel, a longitudinal slot in the barrel, a block of insulating material in the slot, a groove on the inside of the block in the whole length of the barrel and circuit-breakers in the groove said circuitbreakers being electrically connected with the solenoid-windings.

5. In an electromagnetic gun, in combination, a barrel of non-magnetic material, a longitudinal slot in the barrel, a block of insu- IOO IOS

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lating material in the slot, parallel grooves inA the block in the whole length of 'the barrel, elementary solenoids placed on the barrel and connected with the source of electricity, and circuit-breakers in the grooves of said block, servingto close and open the circuit of each solenoid or group of solenoids.

6. In an electromagnetic gun, in combination, a barrel, a longitudinal slot in the barrel, a block of insulating material in the said slot, elementary solenoids placed on the barrel, circuit-breakers mounted on the block, and serving to close and open the circuit of each solen- 01d, and electrical connections between groups of solenoids and the source of electricity and circuit-breakers in the said electrical connection.

7. In an electromagnetic gun the combination, with the projectile, the barrel and a block of insulating material placed in a longitudinal slot in thewhole length of the barrel, of a rod or rods of insulating material fitting into a groove or grooves in the said block and means lhand in presence of two witnesses.

KRISTIAN BIRKELAND.

Witnesses:

ALFREDv J. BRYN, J OH. VAALER. 

